Effects of a concurrent task on fixed-interval responding in humans.

BOWER et al. (1963) asked college students to press a button on a fixed-interval schedule. Every 60 seconds the first press paid a nickel.

While they worked, the students also had to do fast subtraction problems. The math ran at the same time as the button task.

The team wanted to see if the extra mental load would wreck the smooth scallop pattern people usually show on FI schedules.

The subtraction job wiped out the normal pause-and-run shape. Instead of waiting after each nickel, students pressed at a flat, steady rate.

Without quiet time to count or talk to themselves, the clock-like FI pattern disappeared.

Dews (1966) seems to disagree. Pigeons kept the scallop even when most of the interval was filled with an extinction stimulus. Birds don’t count, yet the schedule still ruled their timing.

The clash is simple: humans need verbal mediation; pigeons don’t. Take away the students’ inner speech and the pattern falls apart. Take away almost everything from the birds and the pattern stays.

Emmelkamp et al. (1986) extend the idea. They built FI-like scallops on a conjunctive schedule just by tightening response-reinforcer contiguity. Schedule design, not species habits, can also create the pause-and-run shape.

If your learner uses self-talk to wait for reinforcement, don’t pile on extra tasks. A second demand can erase the wait-and-work rhythm you trained. Run cold-probe trials in silence, or space demands so the learner can still count, sing, or talk inside.